kuhner



March 31, 1964 M. H. KUHNER 3,126,945

REGENERATIVE AIR HEATER Filed March 19, 1962 2 Sheets-Sheet 1 FIG. I

MAX H. K UHNER INVENTOR.

March 31, 1964 M. H. KUHNER 3,126,945

REGENERATIVE AIR HEATER Filed March 19, 1962 2 Sheets-Sheet 2 FIG. 5

MAX H. KUH/VE'R I NVENTOR.

United States Patent 3,126,945 REGENERATIVE AIR HEATER Max H. Kuhner, Oakharn, Mass, assignor to Riley Stoker Corporation, Worcester, Mass, a corporation of Massachusetts Filed Mar. 19, 1962, Ser. No. 180,611 3 Claims. (Cl. 165-6) This invention relates to a regenerative air heater and more particularly to apparatus arranged to increase the temperature of combustion air flowing to a steam generating unit by heat exchange with the hot products of combustion leaving the unit.

In the operation of a steam generating unit, it is quite important that, in order to maintain high efiiciency, as much heat as possible be removed from the outgoing products of combustion. At the same time, it is necessary that the air which is to be used in the combustion process be as warm as possible. For this purpose, it is a practice to use an air heater, either of the tubular recuperative type or the regenerative type. Regenerative air heaters have generally been of a rotary type in which a disk-like wheel carrying heat absorption elements is rotated first into the path of the outgoing products of combustion and then into the path of the incoming combustion air to bring about heat exchange between the two gases. The flow of gas or air through the wheel is parallel to the axis so that, upon an increase of capacity of the steam generating unit, lengthening the thickness of the disk or wheel in the direction of the axis is generally inetfective to handle the larger amounts of products of combustion and combustion air which are involved. It is, therefore, necessary to increase the diameter of the wheel with increased problems of support and space use. The operation of such a large rotary air heater becomes increasingly difficult at higher capacities and the capital cost of the equipment increases much faster than the load capacity. These and other ditficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide a regenerative air heater of high thermal exchange efficiency.

Another object of this invention is the provision of a regenerative air heater which is inexpensive to manufacture and whose capital cost increases only in approximately direct proportion to the load capacity.

A further object of the present invention is the provision of a regenerative air heater whose heat absorptive elements may be quickly removed and replaced.

It is another object of the invention to provide a regenerative air heater which effectively and continuously removes dust from the hot products of combustion of a steam generating unit.

It is a further object of the invention to provide a regenerative air heater whose capacity may be increased by enlarging it in the same direction as the increase in dimension (due to increase of capacity) of the steam generating unit with which it is used.

A still further object of this invention is the provision of a regenerative air heater whose capacity may be increased without increasing the resistance to gas and air flow and without increasing the length of time that it takes an increment of gas or air to pass over the heat absorptive elements.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

The character of the invention, however, may be best understood by reference to one of its structural forms as illustrated by the accompanying drawings in which:

FIG. 1 is a vertical sectional view through an air heater embodying the principles of the present invention and a steam generating unit with which it is used;

FIG. 2 is an enlarged vertical sectional view of the air heater;

FIG. 3 is an enlarged portion of the air heater;

FIG. 4 is an enlarged portion of another part of the air heater; and

FIG. 5 is a sectional view of the heater taken on the line VV of FIG. 3;

Referring first to FIG. 1, it can be seen that the air heater, indicated generally by the reference numeral 10, is shown in use with a steam generating unit 11. The air heater consists of an insulated sheet metal housing 12 having a gas inlet 13, a gas outlet 14, an air inlet 15, and an air outlet 16. Within the housing lies a flexible member 17 formed in a loop and carrying a plurality of heat absorptive members 18. The upper end of the flexible member is supported and driven by a driven sprocket wheel 19 which is driven by a motor 21; at its lower end the flexible member passes around an idler sprocket wheel 22. As is evident in FIG. 1, the flexible member and its associated heat absorptive members 18 forms an elongated loop whose major dimension is vertical. Underlying the lower end and mounted on the housing 12 is a dust hopper 23. Attached to the air inlet 15 is a forced draft fan 24 and attached to the gas outlet 14 is a stack The steam generating unit 11 is provided with a front wall 26, a rear wall 27, and side walls 28 defining a vertically-elongated combustion chamber 29. The front wall 26 is provided with an abutment 2% on which is mounted a directional flame burner 31, while the rear wall 27 is provided with a similar abutment 32 on which is mounted a directional flame burner 33. The burners and combustion chamber are similar to those shown and described in the patent of Craig No. 2,853,059, the abutments 29 and 32 forming a high-temperature, lower cell at the bottom part of the furnace in which combustion is substantially completed. The furnace is an extruded shape, i.e., the cross-section is the same from side Wall to side wall. The burners 31 and 33 are connected by suitable ducting to the air outlet 16 of the air heater 1t) and a fiyash reinjection line 30 extends from the dust hopper 23 to the burner 33 and is provided with a gastight valve 68.

The steam generating unit 11 is provided with a steamand-water drum 33 into which feed water is introduced. Extending downwardly from the drum is a downcomer 34 leading to lower transverse headers 35 and 46. Waterwall tubes leave the header 35 and extend upwardly along the front wall 26, eventually discharging into the steamand-water drum. Other water-wall tubes leave the header, extend up the back wall 27, extend along the underside of the roof, and discharge into the drum. Underneath each side wall 28 is a side wall header 60 to which the downcomer 34 is connected; water-wall tubes extend upwardly from this header 60 to a collector header 36 at the upper part of the furnace which discharges into the drum also. At the upper part of the combustion chamber 29 the front wall 26 is formed with a nose 37, while a similar inwardly-directed nose 38 is formed in the rear wall 27. These noses define a reduced gas offtake 39 leading to a convection pass 41. The convection pass is divided by a central wall 42 into a forward portion 43 and a rearward portion 44. At the lower end of the wall 42 is a superheater header 45 which is attached to superheater platens 46. These platens are connected to a convection superheater 47. Overlying the convection superheater 47 in the forward portion 43 of the convection pass is a low-temperature superheater 48 which is connected to the upper part of the drum 33 to receive steam therefrom. At the top part of the rearward portion 44 of the convection pass is a low-temperature reheater 49 and underlying it a high-temperature reheater 51. Both the forward portion 43 and the rearward portion 44 curve and extend downwardly rearwardly of the rear wall 27 and are provided with suitable dampers regulating the flow of gas through the two portions. Extending across both portions is an economizer 52. Both passes are connected to the gas inlet 13 of the air heater.

Referring to FIG. 2, it can be seen that the air heater 10 is constructed with the driven sprocket wheel 19 out of the path of the gas as it flows from the gas inlet 13 to the gas outlet 14. The flexible member 17 consists of a plurality of metal chains arranged in loops lying in parallal spaced planes. The dimension of the heater perpendicular to the planes is the same as the distance from one side wall 28 of the steam generating unit to the other, so that the air heater extends entirely across the rear wall 27 of the steam generating unit. Attached to the chain and extending at right angles to the planes thereof are a series of mounting bars 53 hingedly attached to the chains and each carrying a heat absorptive member 18. Extending across the housing in the direction of the axis of the shaft on which the driven sprocket wheels 19 are mounted is a wall 58. Each end of the wall is provided with a seal which engages the inside surface of the flexible member 17. Similar seals are provided engaging the outer surfaces of the heat absorptive members adjacent the gas inlet 13 and the gas outlet 14. Such seals are also provided at the other end of the air heater. The side wall of the housing 12 is provided with an access door 54 located in a portion of the housing outside of the projections of the gas and air inlets and outlets. The door is large enough to permit the removal and replacement of a heat absorptive member 18.

Referring now to FIG. 3, it can be seen that each flexible member 17 consists of a chain formed of metallic links 55 joined by pins 56, each mounting bar 53 being hingedly mounted on such a pin 56. The heat absorptive member 18 consists of a series of generally parallel, spaced, corrugated metal plates which are held together by welding, the junction taking place by small metal strips interposed between the various plates. Each member is formed with a groove 57 of T-shape which exactly fits the T-shaped cross section of the mounting bar 53. The heat absorptive member is Welded, or otherwise suitably fastened to the bar.

In FIG. 4 is shown a typical seal 58 which is suitably attached by a hinge block 59 to a wall of the housing 12 of the air heater. A leaf spring 61 biases the seal 58 outwardly so that it engages with suitable pressure with the surface which is to be sealed.

' In FIG. can be seen the manner in which each mounting bar 53 and its heat absorptive member 18 is mounted on a chain or flexible member 17. It can be seen that the plates 55 of the. chain reside on either side of a sprocket wheel 19 and are joined by a roller 62 which, in turn, is mounted on the pin 56 which joinsthe links of the chain together. Mounted on the pin on either side of the chain are locking blocks 63 and 64. Engaging these locking blocks are a flange 65. The construction and operation of this method of attaching the mounting bar to the chain is described in detail in the patent of Rivers No. 2,804,834. Suifice to say that the bar may be readily removed by merely removing looking pins 66 and 67 in the manner described in that patent.

The operation of the invention will now be readily understood in view of the above description. The operation of the furnace and boiler is more or less conventional in that fuel and air are admitted. into the high-temperature lower cell of the furnace through the burners 31 and 33 mounted on the lower surfaces of the abutments 29 and 32. Combustion is substantially completed inthis lower cell and the gases pass upwardly through the combustion chamber 29, giving off heat by radiation to the water flowing in the Water-wall tubes. The hot products of combustion pass through the gas offtake 39, transmitting heat by radiation and convection to the superheater platens 46. Some of the gas goes upwardly through the forward portion 43 of the convection pass, while the remainder flows upwardly through the rearward portion 44. That gas which passes through the forward portion 43 passes over the convection superheater 47 and over the low-temperature superheater 48 to a pass under the roof of the steam generating unit and eventually flows over the economizer '52 under the control of the damper in the 'backpass. The gas which passes through the rearward portion 44 of the convection pass goes over the high-temperature reheater 51 and then over the low-temperature reheater 49 before passing over the rear wall into a back pass where it is under the control of the damper and where it passes over another portion of the economizer 52. The two gases come together again and enter the air heater 10 through the gas inlet 13, flowing out again through the gas outlet 14 into the stack 25. Air is provided for the burners 31 and 33- by a forced draft fan 24 which causes air to flow to the air inlet 15 of the air heater, through the air heater and out through the air outlet 16 from whence it passes to the burners 31 and 33 for combustion. It can be seen, particularly from inspection of FIG. 1, that the heat absorptive members 18 allow the gas and air to flow through them, since, when these members pass through the gas and air flow, the corrugated plates are arranged with their spaces in the line of flow; the corrugations, of course, cause an intense scrubbing action between either the gas or the air, on the one hand, and the metal in the plates, on the other hand, so that heat transfer is quite good. It will be understood, also that the flexible member 17 is made up of a limited number of link chains which are widely spaced.

across the width of the belt and are joined only by the mounting bars 53 and the heat absorption members 18,

so that the air is free to flow through the runs of the loop with only a slight resistance presented by the presence of chains and bars. The chains are driven by the drive sprocket 19 and pass around the idler sprockets 22, there being a drive sprocket and idler sprocket for each chain. The lengths of the shafts on which the sprocket Wheels are mounted, the bars 53, and the heat absorption members 18 are substantially the same as the distance from side wall 28 toside wall 28- of the furnace, so that the air heater is coextensive with the furnace in this direction. It is the nature of this invention that a particular heat absorption member 18 passes through the flow of gas from the furnace twice, once going up and once coming down from the drive sprocket and then passes through the air which is approaching the furnace twice, once going down around the idler sprocket 22 and once coming back up again.

One of the interesting features of the present invention is that the corrugations and the small baffle-like spacer blocks which hold the corrugated plates of the heat ab sorptive members 18 together cause a deposit of dust and flyash from the gas leaving the furnace. This collection of dust is carried downwardly in the loop and a certain amount of the time dust is returned to the furnace along with the combustion air. This has the effect of reducing the dust to a slag which flows out of the furnace in a concentrated form and is readily disposed of. The coarse particles of dust fall from the plates of the heat absorption membersas the loop passes around the bottom of the idler sprocket 22 and are collected in the dust hopper 23. From there, the fiyash passes through the rotatable valves 68 and through the line 30 to the burner 33 where It is introduced with the fuel and air into the furnace and 1s slagged. Furthermore, if there is any combustible left in this dust, it has an added opportunity to be burned, thus increasing the efficiency of the furnace.

The capacity of the air heater may be increased, of course, by increasing the length of the heat absorptive members 18, i.e., the distance by which they extend from the chain belt and the mounting bars 53. There is, of course, a mechanical limitation to this length, since these heat absorption members are supported in a cantilever manner during the vertical runs along the loop. However, there is no appreciable limitation to the vertical height of the air heater and the ideal situation is such that the nature of the heat absorptive members 18 and the vertical height of the air heater are selected so that a standard design and size in the vertical loop dimension may be used. In that way, in order to increase the capacity of the air heater to meet the requirements of the furnace and boiler, it is only necessary that the width of the belt be changed, that is to say, its dimension in the direction of the shafts on which the sprocket wheels are mounted- It is the nature of the particular furnace and boiler arrangement shown and described in the specification that its steam generating capacity may be increased merely by increasing the distance between the side walls 28. The longitudinal vertical cross section remains the same. It is in the contemplation of the invention that the steam generating unit includes a furnace and boiler arrangement of this type along with an air heater such that a standard design of cross-section (similar to that shown in FIG. 1) may be used and that the capacity of the entire unit may be increased only by increasing the dimension perpendicular to the plane of FIG. 1, i.e., the dimension from side wall 28 to side wall 28 and the width of the flexible member 17.

It also should be noted, in connection with the removal of heat from the gas which is flowing to the stack 25 and the heating of the air which is flowing to the furnace from the forced draft fan 24, that either of these functions may be adjusted by adjusting the proportions which they occupy of the vertical height of the air heater. In other words, it may be necessary, to meet the demands of a particular installation, that the vertical heights subtended by the inlet and outlet air passages be substantially twice that subtended by the gas flow. It will be normal, however, to use as much air heating capacity as is economically feasible to reduce the gas temperature as low as possible, the present air heater being relatively free of the problem of deterioration due to condensation of sulphuric acid and the like from the products of combustion passing to the gas. That is to say, even though the gas temperature is reduced to a point below the dew point or the point when such volatile chemicals condense from the gas. In case a particular heat absorptive member becomes deteriorated, however, and needs to be replaced, it is only necessary to stop the air heater for a short time, open the access door 54 in the housing 12, and remove and replace a heat absorptive member 18.

The heat absorptive member is removed along with its mounting bar 53 by removal of locking pins 66 and 67 and lifting vertically away from the chain and sprocket wheel. Because of the seals which exist between the walls of the housing 12 and the heat absorptive members and those which exist between the wall 50 and the inside of the chains, there is very little flow of gas upwardly in the area of the loop around the drive sprocket wheel 19. This makes the job of removing and replacing heat absorptive members much easier and it also protects the shaft and sprocket mountings.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by letters Patent is:

1. A regenerative air heater, comprising a housing having a gas inlet, a gas outlet, an air inlet and an air outlet, the gas inlet and the gas outlet being aligned, the air inlet and the air outlet being aligned and spaced from the gas inlet and outlet, an endless flexible member mounted in the housing and forming an elongated loop, the gas and air passing from the inlets to the outlets in paths perpendicular to the length of the loop, the flexible member consisting of a plurality of endless chains lying in spaced parallel planes, a plurality of mounting bars joining the chains and removable therefrom, each mounting bar extending at a right angle to the said planes, one portion of the loop passing between the gas inlet and the gas outlet, another portion of the loop passing between the air inlet and the air outlet, a heat absorptive member attached to each mounting bar and movable therewith, the chains extending around driven sprocket wheels at one end of the loop and around idler sprocket wheels at the other end of the loop, the sprocket wheels residing in portions of the housing outside of the projections of the inlets and outlets on the loop, resiliently-biased seals located on the housing and engaging the heat absorptive members to prevent flow of gas and air between the gas inlet and outlet on the one hand and the air inlet and outlet on the other hand, the heat absorptive members being formed of a plurality of closely-spaced generally-parallel corrugated sheet metal elements adapted to trap dust, a dust hopper underlying one end of the loop in an area of reversal of movement of the heat absorptive members, and means forming an access door in the housing at a location on a projection of the path of movement of the members onto a portion of the housing extending parallel to the said planes, the access door being of a size permitting the removal of a heat-absorptive member.

2. A regenerative air heater, comprising (a) a housing having a gas inlet, a gas outlet, an air inlet, and an air outlet, the gas inlet and the gas outlet being aligned, the air inlet and the air outlet being aligned and spaced from the gas inlet and outlet,

(b) an endless flexible member mounted in the housing and forming an elongated loop, one portion of the loop passing between the gas inlet and the gas outlet, another portion of the loop passing between the air inlet and the air outlet,

(0) heat-absorptive members attached to the flexible members, means associated with each heat-absorptive member permitting ready removability of the member from the flexible member, and

(d) an access door provided in the housing at a location on a projection of the path of movement of the members onto a portion of the housing extending parallel to the said planes, the access door being of a size permitting the removal of a heat-absorptive member.

3. A regenerative air heater as recited in claim 2wherein each chain consists of a series of elongated plates joined by pins, each mounting bar being connected to a pin for hinged motion, a readily-releasable means being used to connect each bar to its pin, each mounting bar having a generally T-shaped cross-section and each heat-absorptive member being provided with a T-shaped groove of substantially the same cross-section as the said mounting bar to constitute the main connection between the bar and the member.

References Cited in the file of this patent UNITED STATES PATENTS 1,697,591 Dowd Jan. 1, 1929 1,843,252 Toensfeldt Feb. 2, 1952 2,832,323 Craig Apr. 29, 1958 2,947,289 Miller Aug. 2, 1960 FOREIGN PATENTS 89,244 Austria Aug. 25, 1922 116,544 Austria Feb. 25, 1930 251,895 Great Britain May 13, 1926 789,970 Great Britain Jan. 29, 1958 

1. A REGENERATIVE AIR HEATER, COMPRISING A HOUSING HAVING A GAS INLET, A GAS OUTLET, AN AIR INLET AND AN AIR OUTLET, THE GAS INLET AND THE GAS OUTLET BEING ALIGNED, THE AIR INLET AND THE AIR OUTLET BEING ALIGNED AND SPACED FROM THE GAS INLET AND OUTLET, AN ENDLESS FLEXIBLE MEMBER MOUNTED IN THE HOUSING AND FORMING AN ELONGATED LOOP, THE GAS AND AIR PASSING FROM THE INLETS TO THE OUTLETS IN PATHS PERPENDICULAR TO THE LENGTH OF THE LOOP, THE FLEXIBLE MEMBER CONSISTING OF A PLURALITY OF ENDLESS CHAINS LYING IN SPACED PARALLEL PLANES, A PLURALITY OF MOUNTING BARS JOINING THE CHAINS AND REMOVABLE THEREFROM, EACH MOUNTING BAR EXTENDING AT A RIGHT ANGLE TO THE SAID PLANES, ONE PORTION OF THE LOOP PASSING BETWEEN THE GAS INLET AND THE GAS OUTLET, ANOTHER PORTION OF THE LOOP PASSING BETWEEN THE AIR INLET AND THE AIR OUTLET, A HEAT ABSORPTIVE MEMBER ATTACHED TO EACH MOUNTING BAR AND MOVABLE THEREWITH, THE CHAINS EXTENDING AROUND DRIVEN SPROCKET WHEELS AT ONE END OF THE LOOP AND AROUND IDLER SPROCKET WHEELS AT THE OTHER END OF THE LOOP, THE SPROCKET WHEELS RESIDING IN PORTIONS OF THE HOUSING OUTSIDE OF THE PROJECTIONS OF THE INLETS AND OUTLETS ON THE LOOP, RESILIENTLY-BIASED SEALS LOCATED ON THE HOUSING AND ENGAGING THE HEAT ABSORPTIVE MEMBERS TO PREVENT FLOW OF GAS AND AIR BETWEEN THE GAS INLET AND OUTLET 